Biodiversity and ecosystem function and the design of tallgrass restorations for biomass production

Biodiversity and ecosystem function research (BEF) suggests species richness may provide high levels of ecosystem functions. However, few studies have applied a BEF perspective of restoration, which utilizes biodiversity to achieve increases in ecosystem functions. In this study, we test the application of the BEF perspective of restoration in the design of tallgrass prairie plantings as a biomass crops. Specifically, we examine the effects of planted species richness on biomass production, resistance to disturbance, and resistance to invasion by weeds. Four seed mixes which range in species richness (1, 5, 16 and 32 species) were established in four, field-scale (0.33-0.55 ha) plots on three soil types. Over four years, the seed mixes produced similar amounts of biomass (8.27 ± 0.65 to 7.46 ± 0.65 Mg/ha). Seed mixes had relatively high yields compared to estimates from fertilized monocultures of perennial crops in the region. Species rich planting (16-32 species) may produce more biomass than less species rich plantings in years without flooding or drought. However, the effects of species richness on productivity are complicated by soil type. The mix with the highest species richness (32 species) had the lowest biomass production on the Waukee loam soil, but the highest biomass production on Spillville-Coland clay loam soil. Plantings with higher species richness were also less resistant to drought. However, species rich mixes (16 and 32 species) produced similar amounts of biomass compared to less species rich mixes (5 species) with the same dominant species. Finally, I found that increased species richness increased resistance to invasion by weeds and as few as five species may provide high levels of resistance to invasion by weeds. The study suggests that the application of the BEF perspective of restoration may lead to weed resistant crops which are as productive, or more productive than low diversity crops. BIODIVERSITY AND ECOSYSTEM FUNCTION AND THE DESIGN OF TALLGRASS RESTORATIONS FOR BIOMASS PRODUCTION A Thesis Submitted in Partial Fulfillment of the Requirements for the Degree Master of Science Dustin Robert Jon Graham University of Northern Iowa May, 2015